Enhanced Status Code 5.2.3: Message Length Exceeds Administrative Limit

Permanent failure Medium severity Content RFC 3463

What it means

Enhanced Status Code 5.2.3 means “Message Length Exceeds Administrative Limit.” Your email exceeds the maximum message size allowed by the recipient server. This includes all content: headers, body text, HTML, and attachments after Base64 encoding. Reduce the message size or use file sharing links.

At a glance

Code5.2.3

Bounce typeHard (permanent)

SeverityMedium

CategoryContent

What to doSuppress the address; do not retry

StandardRFC 3463

What it looks like in your mail logs

Remote Server returned '550 5.2.3 RESOLVER.RST.RecipSizeLimit; message too large for this recipient'

What does 5.2.3 mean?

Enhanced status code 5.2.3 is functionally similar to SMTP code 552 and indicates your message exceeds the size limit set by the recipient mail server or organization. The limit varies by provider - Gmail accepts 25MB, some corporate servers may limit to 10MB or less.

Remember that Base64 encoding increases attachment sizes by approximately 33%. A 20MB file becomes about 27MB after encoding. Additionally, HTML emails with many embedded images can be surprisingly large. Always check total message size including encoding overhead.

How 5.2.3 plays out

Your server attempts delivery

The recipient server returns a permanent 5.2.3 rejection

This is a hard bounce: the message will not be accepted as sent

Suppress the address and fix the root cause before resending

Where 5.2.3 sits: soft vs hard bounce

	Soft bounce (4xx)	Hard bounce (5xx)
Nature	Temporary	Permanent
SMTP class	`4xx`	`5xx`
What to do	Let it retry	Suppress the address
Recoverable?	Often	No
5.2.3 is		✓ this code

Common causes of 5.2.3

Attachments too large for the recipient server limit
HTML email with many embedded images
Base64 encoding overhead pushing message over the limit
Organization has set restrictive size limits

How to fix 5.2.3

Reduce attachment sizes - compress files or lower image resolution
Use cloud file sharing links instead of attachments
Strip unnecessary embedded images from HTML templates
Check the recipient server SIZE parameter in the EHLO response

Frequently asked questions

What does bounce code 5.2.3 "Message too large" mean?

Bounce code 5.2.3 means your email exceeded the per-mailbox message size limit set by the recipient's administrator. This is distinct from the system-wide size limit (5.3.4); it applies to a specific mailbox that has a stricter size restriction than the server's general limit. The email cannot be delivered in its current size and must be reduced before resending.

How do I fix a 5.2.3 email bounce?

Reduce your email's total size by compressing attachments, using cloud storage links (Google Drive, OneDrive, Dropbox) instead of direct attachments, or splitting the message into multiple smaller emails. Remember that MIME encoding increases actual message size by approximately 37% over the raw file size, so a 25 MB attachment becomes roughly 34 MB in transit. Contact the recipient to confirm their specific size limit and adjust accordingly.

What is the difference between 5.2.3 and 5.3.4?

Error 5.2.3 indicates the message exceeded a per-mailbox administrative size limit specific to the recipient's account, while 5.3.4 indicates the message exceeded the entire mail system's fixed maximum size. In practice, 5.2.3 means the specific recipient has a lower size limit than the server default, while 5.3.4 means the message is too large for the server overall. Both require reducing message size, but 5.2.3 may only affect certain recipients on the same server.

Related bounce codes

Sources & further reading

RFC 3463 · The standard that defines this reply code Microsoft Learn, Configure message size limits for a mailbox · Reference for the per-mailbox send and receive size limits that produce this RecipSizeLimit NDR.

Reviewed by Jennifer Jackson, Email Deliverability Analyst · June 2026 ← All bounce codes